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Page 21 | AlliedWare™ OS How To Note: IGMP
IGMP proxy > Example
IGMP proxy
In very simple tree-design networks, IGMP Proxy is a useful simple alternative to a multicast
routing protocol for multicasting between VLANs.
An IGMP Proxy sends IGMP Membership Report and Leave group messages to an upstream
subnetwork on behalf of downstream devices, and sends Queries downstream. In other
words, an IGMP Proxy effectively ferries IGMP messages from one VLAN to another. The
IGMP Proxy looks like an IGMP Querier to the downstream VLAN, and like a client to the
upstream VLAN. Note that the Proxy can only have one configured upstream VLAN.
IGMP Proxy is available on all Allied Telesis routers and managed layer 3 switches except
AT-9800 and SwitchBlade series. For AT-8948, AT-9900 and x900-48 series switches, it
requires software version 2.8.
1
or later.
If you use IGMP Proxy on a switch, multicast data packets are processed by the CPU so are
not forwarded at wirespeed.
Example
IGMP Proxy only works in tree networks, so for this example we convert the network from
a loop into a tree by disabling port 50 on the AT-8948 switch.
Switch 3 is the IGMP Proxy. Switch
1
is upstream of the Proxy. Switch 2 is downstream of the
Proxy on vlan
1
00. Therefore, the multicast server and client
1
are now in different VLANs
and switch 3 sits on the boundary between the two VLANs. This network is shown in the
following figure.
Multicast Server
AT-8948
Switch 1:
Querier
Rapier 24i
Switch 2:
Snooper
C
li
e
n
t
1
Rapier 24i
Switch 3:
Proxy
port 1
vlan200
port 2
port 25 port 25
port 26
port 49
upstream
vlan200
downstream
vlan100
igmp-proxy.eps